1. Field of the Invention
This invention pertains to dispensing medical or physiological substances or matter internally and more specifically to the mechanism used in implanted apparatus for dispensing these substances.
2. Description of the Prior Art
A review of prior art practices with regard to dispensing medical substances internally of the body is given in my prior U.S. Pat. No. 3,692,027 to which reference is made. So far as I am aware, my prior U.S. Pat. No. 3,692,027 provides the first teaching of a self-powered device which can be implanted and which is adapted to dispense medical substances in pre-measured doses at specific intervals over a long period of time. There has appeared in the June 1973 issue of Fortune magazine an article describing other continuous diffusion capsule types of dispensing devices. This article points out and emphasizes the tremendous need for long term medication dispensing devices which can provide for dispensing of medication at specific target organs or target sites. The prior art in the area of diffusion devices is also illustrated in Patent No. 3,379,996 by David Long and Moses Folkman for a polysiloxane carrier for controlled release of drugs and other agents. The device of this patent consists of a silicone rubber container with the drug being soluble and capable of diffusing through the silicone rubber to the outer surface of the container. A further development of this device was reported in the literature in the Annals of the New York Academy of Sciences, vol. 111, 1963-64 on pages 857-868 by Judah Folkman and David Long in which an electrical voltage is described as being applied to the container and to an outside electrode, in an attempt to increase the diffusion of materials through the fibrous scar tissue which is caused to be thrown up around the container by reason of its being implanted into the myocardium. The medication is described as being pulled through the myocardial fibrous scar tissue by means of iontophoresis. In these adaptations, the medication is in a continuous diffusion state and is not presented in discrete doses at timed intervals or according to the physiological needs.
Related to the present invention is the practice of implanting devices which sense heart conditions by means of the cardiac electrical activity and trigger electrical pulses to effect the heart rate according to the sensed data. These devices have generally been categorized a "pacemakers" and their use proves that the human body can accept implanted devices without endangering human life in the implantation procedure. They have also provided documentation for the applicability of feedback in the instance of the demand pacemaker version in which the output is controlled by the pacemaker logic which makes decisions on the basis of the electrical activity of the heart. The feasibility of the demand pacemaker for implantation is documented in the articles listed below.
1. Goetz, R. H.; Goldstein, J. V.; Frater, R. W. M., Berkovits, B. -- "Demand Pacemaking in Intermittant Heart-Block," Journal of the American Medical Association, Vol. 10, pp. 657-662, 1968.
2. Nathan, D. A.; Center, S.; Wu, C.; Keller, W.; "An Implantable, Synchronous Pacemaker for the Long Term Correction of Complete Heart-Block." Circulation, Vol. XXVII, pp. 682-685, 1963.
3. Fischler, H.; Barr, I. M.; Auerback, Yerushalmi S.; Neufeld, H. N. -- "Atrial-Synchronized Demand Heart Pacing." IEEE Transactions on Biomedical Engineering, Vol. BME-16, pp. 64-69.
A further area of the prior art related to the invention concerns the various types of sensors some of which are now commercially available and which can be used to accurately sense physiological and chemical body conditions. At present, the output of most of these devices that sense body changes are recorded and/or acted on by devices external to the body. For example, glucose detection, pH detection, ionic change detection, blood pressure or blood flow detection, electrical activity detection, respiratory detection, and gastrointestinal motility detection all constitute existing practical types of sensing apparatus.
It should also be recognized that the prior art has shown that an implanted device having a battery supply can be electrically recharged without having to remove the device. Also, my own U.S. Pat. No. 3,692,027 refers to means for recharging an implanted medication supply. Thus, both implanted battery and medication storage recharging are known.
From the foregoing, it can be seen that while the implanting technique has been perfected in many respects, and that while both the diffusion device which releases medication continuously and my own self-powered technique which provides a means for dispensing medical substances in pre-measured doses on a continuous basis or at predetermined regular intervals, no dispensing device or method has appeared in the prior art which allows medical substances to be dispensed by an implanted device and according to specific physical requirements of the patient that are determined by the device itself.